Digital trim capacitor programming

ABSTRACT

A programming method ( 250 ) for digitally programming the adjustment of an electronic trim capacitor ( 212, 314, 414 ). In an initial step ( 252 ), programming is initiated by setting an enable terminal ( 224 ). In subsequent steps ( 254, 256 ) a pulse signal ( 226 ) then applied to a program terminal ( 222 ) and the number of pulses ( 228 ) provided to the programming terminal ( 222 ) while the enable terminal ( 224 ) is set determines the total number of capacitance increments for which the electronic trim capacitor ( 212, 314, 414 ) is programmed. The electronic trim capacitor ( 212, 314, 414 ) may be incorporated into an integrated circuit ( 12, 312 ) or a module ( 412 ) and the electronic trim capacitor ( 212, 314, 414 ) may be programmed and used “in situ” in a more general circuit ( 1 ) such as an oscillator ( 301 ) or an amplifier ( 401 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of application No. Ser. 09/490,599, filedJan. 25, 2000.

TECHNICAL FIELD

The present invention relates generally to electrical capacitors whichmay be variably set or trimmed, and more particularly to methods ofprogrammably adjusting such capacitors to a desired value of capacitanceelectronically rather than mechanically. It is anticipated that aprimary application of the present invention will be for adjusting ortuning such electronically programmable capacitors either before orduring their use within more general electronic circuits.

BACKGROUND ART

Many electronic circuits require adjustment of particular parameters,either during initial assembly or later, as changing conditions ordeterioration due to age, etc. affect such parameters. Of presentinterest is capacitance, since setting capacitance is criticallyimportant to insure the proper operation of a wide variety of electricalcircuits and circuit-based processes which are in wide use. Capacitancemay, of course, be set by making an initial choice of or performingreplacement with a fixed-value component. This will generally not bedealt with here, but it should be kept in mind that substituting anadjustable capacitor for a fixed-value one may be useful in manysituations.

Capacitors which may be variably adjusted are desirable, or evencritically necessary, in many electronic circuits. For example,computers, clocks, radios, televisions, garage door openers, and amyriad of other electronic devices all have one or more internalcircuits that require correct capacitance value adjustment. Adjustingcapacitance to achieve such values can be done at the time of initialassembly, where it is almost always necessary, or it can be done laterby readjusting back to the original value or by changing to an entirelynew capacitance value, as appropriate.

For purposes of the following discussion, the operation of adjusting avariable capacitance device is collectively termed “trimming,”regardless of the specific device type. Further, the operation ofsetting a variable capacitance device within a more general circuit iscollectively termed “tuning.” It should be appreciated that thesedefinitions are broad and widely encompassing ones. For example, whilesome might consider tuning to be proprietary to operations in particularindustry segments, such as the adjustment of radio frequency oscillatorsand amplifiers, and to therefore not also encompass operations likesetting delay circuits or stabilizing digital memories, such restrictiveinterpretation is not intended and is not appropriate here.

Tuning requires determining what capacitance value will be correct in acircuit, and then providing and trimming a “tuning capacitor” in thecircuit to that value. Unfortunately, this can be an expensive,time-consuming, and error prone process.

FIG. 1 (background art) is a diagram depicting a general circuit 1requiring capacitive tuning. A conventional analog tuning device 2 isconnected to the general circuit 1 for this purpose. The analog tuningdevice 2 may be as simple as a standard adjustable capacitor, or it maybe a complex assembly used to achieve the net effect of adjustingcapacitance.

FIG. 2 (background art) depicts the usual choice made today for theanalog tuning device 2, a variable analog capacitor 3. Presently themost commonly used variable analog capacitors 3 are mechanical innature. For example, one type includes several semicircular plates whichare rotated relative to other semicircular plates which are fixed. Theamount by which the respective plates overlap then determines thecapacitance. If the rotating plates do not overlap the fixed plates atall, the capacitance is nominally zero, and if the plates completelyoverlap, the maximum capacitance of the device is reached. Adjusting toany capacitance between zero and the maximum is thus possible.

Unfortunately, this type of variable analog capacitor 3 has a number ofdisadvantages. For example, the mechanical relationships of the platesare much subject to undesirable change by shock and vibration. Other,more subtle, influences on the net capacitance are variation intemperature, pressure, and humidity. The dielectric, or inter-platemedium, in such capacitors is often air or another gas, and must usuallybe kept relatively contained and uncontaminated. Liquid or gel filledadjustable capacitors are also possible but are uncommon, due toconcerns such as fill leakage past the seals around adjustment mechanismshafts, etc. Entirely solid dielectrics are not possible, since theplates must permit movement. In sum, variable analog capacitors 3 havenumerous inherent characteristics that make them unreliable and failureprone.

Another consideration is utility. To adjust or to readjust the variableanalog capacitor 3 requires physical access to perform the mechanicaladjustment operation, which is typically rotation. In large and complexsystems other components and entire other systems may obscure physicalaccess. In small and compact systems such access may also be difficult,and can even subject surrounding components to potential damage. Inhazardous locations, such as the ocean's depths, physical access can bequite difficult, and in remote locations, such as those visited by spaceprobes, physical access can be outright impossible.

Accordingly, what is needed is a new type of trimable capacitor for usein tuning circuits. This new type of capacitor should not employmechanical trimming, preferably being electronically trimable. It shouldalso be physically durable, employing all solid and robust materials. Itis further desirable that this new type of capacitor permit easycapacitance value adjustment and readjustment.

Of paramount importance for new types of electronically trimablecapacitors is the ability to “program” them. Once a suitable trimabledevice is provided, and examples will be presently discussed, thereremains a need to initially adjust this device, and to readjust itscapacitance value as desired. In particular, as digital techniques areincreasingly used in electronic circuits, being able to digitally trimsuch capacitors is highly desirable. Accordingly, what is needed is amethod of digitally programming an electronically trimable capacitor.

DISCLOSURE OF INVENTION

Accordingly, it is an object of the present invention to provide amethod of non-mechanically and digitally programming an electronicallytrimable capacitor.

And another object of the invention is to provide a method ofprogramming an electronically trimable capacitor once it is incorporatedinto a more general circuit, to tune the more general circuit thusemploying it.

Briefly, one preferred embodiment of the present invention is a methodfor digitally programming a capacitance value for an electronicallyadjustable trim capacitor. A program signal to is applied to a programterminal of the adjustable trim capacitor and the capacitance value isset with a logic based on the applied program signal.

An advantage of the present invention is that it does not requirephysical access to the trimable capacitor for the operation of trimmingit, or to a more general circuit employing the trimable capacitor, forthe operation of tuning that more general circuit. Since only electronicaccess is required, trimming and tuning are possible even when physicalaccess is difficult or impossible to obtain, such as within very smallassemblies like cell phones, or when in distant locations like outerspace.

Another advantage of the invention is that it provides a fast method ofprogramming an electronically trimable capacitor, and thus one that isparticularly economical.

Another advantage of the invention is that it provides a reliable methodfor programming an electronically trimable capacitor, and thus one thatis further economical due to the elimination of feedback steps oroverall system problems which may result due to error.

And another advantage of the invention is that it provides a method ofprogramming a trimable capacitor which ensures that programming willoccur only when it is desired. By the use of digital techniques andappropriate signal conditioning, unintentional signals and spuriousinfluences, like electronic noise, can be prevented from inadvertentlymiss-programming the electronically trimable capacitor.

These and other objects and advantages of the present invention willbecome clear to those skilled in the art in view of the description ofthe best presently known mode of carrying out the invention and theindustrial applicability of the preferred embodiment as described hereinand as illustrated in the several figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The purposes and advantages of the present invention will be apparentfrom the following detailed description in conjunction with the appendeddrawings in which:

FIG. 1 (background art) is a block diagram depicting a general circuitrequiring capacitive tuning, along with a conventional analog tuningdevice as is typically used for this purpose;

FIG. 2 (background art) is a schematic diagram depicting the usualchoice of component made today for the analog tuning device of FIG. 1,an adjustable variable analog capacitor 3;

FIG. 3 is a block diagram showing a general circuit requiring capacitivetuning which is connected to a digitally programmable capacitance, or anelectronic trim capacitor, according to the present invention;

FIG. 4 is a block diagram illustrating internal functions of theelectronic trim capacitor of FIG. 3;

FIG. 5 is a block diagram illustrating internal functions of anelectronic trim capacitor that provide values from 0 pico farads (pF) to7 pF, in 1 pF increments;

FIG. 6 is a block diagram illustrating internal functions of anelectronic trim capacitor that provides values from 0 pF to 15 pF, in 1pF increments;

FIG. 7 is a block diagram illustrating internal functions of anelectronic trim capacitor that provides values from 0 pF to 31 pF, in 1pF increments;

FIG. 8 is a schematic depicting a capacitor-based quality factor (Q)enhancing structure being used on a capacitive circuit, with thecombination collectively being used for tuning a general circuit;

FIG. 9 is a schematic depicting a capacitor and inductor-based Qenhancing structure being used on a capacitive circuit, with thecombination collectively being used for tuning a general circuit;

FIG. 10 is a block diagram of an integrated circuit embodiment of anelectronic trim capacitor, such as that of FIGS. 4-7, ready for digitalprogramming while in place within a high Q structure, such as that ofFIG. 8 or 9;

FIG. 11 is a flow chart depicting the major steps for programming theelectronic trim capacitors of FIGS. 4-7 and FIG. 10;

FIG 12 is graph of the capacitance values of the electronic trimcapacitor presented as a function of the digital pulses used to programit;

FIG. 13 is a block diagram illustrating internal functions of acomponent integration of both an electronic trim capacitor and acapacitor-based high Q structure, ready for digital programming to tunean oscillator; and

FIG. 14 is a block diagram illustrating internal functions of acomponent integration of both an electronic trim capacitor and acapacitor and inductor-based high Q structure, ready for digitalprogramming to tune an amplifier.

FIG. 15. illustrates a stylized block diagram of the electronic trimcapacitor with a subset of circuits which provide protection againstprogramming errors.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is a method of digitally programming anelectronically trimable capacitor. As illustrated in the variousdrawings herein, and particularly in the view of FIG. 11, a preferredembodiment of the invention is depicted by the general referencecharacter 250.

“Internal logic” is defined to be any series of procedures or algorithmscontained within a circuit.

FIG. 3 is a block diagram showing an electronic trim capacitor 10connected to a general circuit I requiring a specific capacitance inorder to be tuned correctly. As will presently be described, theelectronic trim capacitor 10 has variable capacitance and can bedigitally set to a specific capacitance needed to tune the generalcircuit 1.

FIG. 4 is a stylized block diagram particularly illustrating internalfunctions of the electronic trim capacitor 10, which here is implementedas an integrated circuit 12. The electronic trim capacitor 10 has afirst power terminal 14 (V_(DD)) and a second power terminal 16(V_(ss)); a first capacitor terminal 18 (C₁) and a second capacitorterminal 20 (C₂); a program terminal 22 (Program); and an enableterminal 24 (Enable). In generally conventional manner for integratedand modular circuits, the first power terminal 14 and the second powerterminal 16 may receive suitable electrical power to operate theelectronic trim capacitor 10. Also in generally conventional manner, thefirst capacitor terminal 18 and the second capacitor terminal 20 connectthe electronic trim capacitor 10 to the general circuit 1. However,unlike any features of pre-existing devices, the program terminal 22 andthe enable terminal 24 here provide the ability to digitally program theelectronic trim capacitor 10 to a desired specific value of capacitance.

As shown in FIG. 4, the integrated circuit 12 of the inventiveelectronic trim capacitor 10 has a number of branch circuits 30, eachincluding a capacitor 32 connected in a series arrangement with one ormore switches 34. In embodiments such as the integrated circuit 12version shown here, the inventor has used solid state MOSFET devices,but this is not a necessary requirement. Within each of the branchcircuits 30, the switches 34 electrically connect or disconnect thecapacitor 32 to the first capacitor terminal 18 and second capacitorterminal 20. The states of the respective switches 34 thereforedetermine whether each branch circuit 30, and thus its respectivecapacitor 32, is connected to the first capacitor terminal 18 and secondcapacitor terminal 20, for use by an outside circuit like the generalcircuit 1 (FIG. 3). When the switches 34 connect the respective branchcircuits 30 in this manner, the respective capacitors 32 are includedinto the total capacitance exhibited at the first capacitor terminal 18and second capacitor terminal 20. Conversely, when a switch 34, or apair of switches 34 as shown here, disconnect a particular branchcircuit 30, the capacitor 32 of that branch circuit 30 is not includedin the total capacitance exhibited by the inventive electronic trimcapacitor 10.

Turning now specifically to the capacitors 32, in the inventor'spresently preferred embodiment these have values represented by theclosed mathematical sequence:

{2^((m−n))c} where 0<n<m; or 2^((m−1))c, . . . , 2c, 1c

where c is a pre-selected constant value of capacitance, and m is thetotal number of branch circuits 30 which are present. Thus, if theelectronic trim capacitor 10 contains three branch circuits 30,providing three capacitors 32 total and making m=3, the respectivecapacitance values would be: 1c, 2c, and 2⁽³⁻¹⁾c, or 4c. Similarly, ifthe electronic trim capacitor 10 contains five branch circuits 30 (seee.g., FIG. 7) the capacitance values would be: 1c; 2c; 4c; 2⁽⁵⁻²⁾c, or8c; and 2⁽⁵⁻¹⁾c, or 16c.

From the preceding it follows that the states of the various switches 34are what determine the total capacitance exhibited by the inventiveelectronic trim capacitor 10 between its first capacitor terminal 18 andits second capacitor terminal 20, and that the capacitance isselectively variable in the general manner of conventional trimcapacitors. Furthermore, by selectively operating the switches 34 tocontrollably connect the various branch circuits 30, the capacitors 32can be combined to produce total capacitance values represented by asecond closed mathematical sequence:

{nc} where 0≦n≦(2^(m)−1); or 0c, 1c, 2c, 3c, . . . (2^(m)−1)c

where c is again the pre-selected constant value of capacitance, and mis again the total number of branch circuits 30 which are present.Having no switches 34 closed provides no capacitance across the firstcapacitor terminal 18 and second capacitor terminal 20, i.e., theleftmost value in the sequence, and having all of the switches 34 closedprovides the maximum capacitance, i.e., the rightmost value in theseries. The capacitance values in between can all be achieved as well.

For example, for an electronic trim capacitor 10 having three branchcircuits 30 using the first sequence above would suggest values of 1c,2c, and 4c for the respective capacitors 32. This would accordinglypermit the electronic trim capacitor 10 to produce any value between 0cand 7c, according to the second sequence above. The value of 1c can beachieved by connecting only the 1c capacitor; 2c can be achieved byconnecting only the 2c capacitor; 3c can be achieved by connecting boththe 1c and 2c capacitors together, since parallel capacitances add(1c+2c=3c); 4c can be achieved by connecting the 4c capacitor only; 5ccan be achieved by connecting the 4c and 1c capacitors together. Thevalue of 6c can be achieved by connecting the 4c and 2c capacitorstogether; and, finally, 7c can be achieved by connecting the 1c, 2c and4c capacitors all together. In similar manner, according to the firstmathematical sequence, if the electronic trim capacitor 10 contains fourcapacitors 32 with the fourth having a value of 8c, any value between 0cand 15c can be achieved.

The total capacitance can thus be selected, in one c unit increments, tobe any amount between nominal zero (ignoring intrinsic effects due tocomponent leads, circuit traces, etc.) and the sum of all of theavailable capacitors 32.

For use in the integrated circuit 12 of FIG. 4, a suitable pre-selectedconstant value of capacitance, c, is one pico farad (pF). An embodimentof this type having three branch circuits 30 (see e.g., FIG. 5) wouldtherefore have 1pF, 2 pF, and 4 pF capacitors 32, and would be able toprovide 0 pF, 1 pF, 2 pF, 3 pF, 4 pF 5 pF, 6 pF or 7 pF of capacitancevalues. Alternately, an embodiment of this type having four branchcircuits 30 (see e.g., FIG. 6) would additionally include an 8 pFcapacitor 32 and additionally provide selectable 8 pF through 15 pFcapacitance values.

Those skilled in the relevant arts will readily appreciate that theinternal capacitors 32 may be combined into other arrangements. Forexample, embodiments using series or series-parallel connections may beconstructed. The capacitors used may also be collectively chosen to meetother mathematical relationships, or even to be governed by noparticular relationship other than producing particularly desirablecombinational results. However, to facilitate discussion the examplesused herein are generally restricted to ones based on simple parallelconnection and ones based on simple binary series relationship.

FIG. 4 also shows how the inventive electronic trim capacitor 10 furtherincludes an interface 36 and a memory 38. The interface 36 serves toprogram the electronic trim capacitor 10 and the memory 38 serves forretaining that programming.

Initial programming of the interface 36 is via the program terminal 22,which connects to the interface 36 and permits providing it withexternal programming instruction. This programming causes the electronictrim capacitor 10 to either connect or disconnect the respective branchcircuits 30, and their respective capacitors 32, across the firstcapacitor terminal 18 and second capacitor terminal 20. It therefore isthe interface 36 which tells each switch 34 what state to be in, open orclosed. And it is this programming via the interface 36 which ultimatelydetermines which capacitors 32 are connected to the first capacitorterminal 18 and second capacitor terminal 20 and what the totalcapacitance of the electronic trim capacitor 10 will be.

The preferred procedure for programming the electronic trim capacitor 10at the program terminal 22 is to first set the enable terminal 24 to aparticular electrical state and to then apply one or more electricalpulses to the program terminal 22. Each of these pulses includes anelectrical transition which causes the interface 36 to set one switch34, or a set of switches 34, to connect or disconnect a branch circuit30 across the first capacitor terminal 18 and second capacitor terminal20. It is anticipated that in most embodiments setting or “enabling”programming at the enable terminal 24 will first operate to reset theelectronic trim capacitor 10 to its minimum capacitance, beforeprogramming ensues, so that programming always starts from that knownstarting point. In the examples presented herein a minimum capacitancestarting point is used, but this is not a requirement and resetting tomid-range or even maximum range values may be appropriate for someapplications. A more detailed discussion of the external programming isnow deferred until discussion of FIGS. 11 and 12, below.

The memory 38 may store a set of state values for all of the switches34. The contents of the memory 38 can then be communicated to theinterface 36 so that it can internally reinstate a previously storedprogram, and thus cause the electronic trim capacitor 10 to againexhibit a previously chosen capacitance across the first capacitorterminal 18 and second capacitor terminal 20. This manner of programmingdoes not require use of the program terminal 22, or generally of anyexternal signals. Instead, in the preferred embodiment, initiallyapplying power to the first power terminal 14 and second power terminal16 may cause the contents of the memory 38 to be used by the interface36 to set the capacitance of the electronic trim capacitor 10. Thisapproach handles normal power-on and power dip situations, but it is nota requirement and more complex methods and additional control terminalscan be used in alternate embodiments.

In many embodiments the memory 38 will preferably be relativelynon-volatile, to permit storing a program of state values for all of theswitches 34 even after power is removed from the first power terminal 14and second power terminal 16 for some time. An EEPROM type memory 38 istherefore a preferred choice, but EPROM, zener, fuse-link, and stillother types may be acceptable in alternate embodiments of the invention.

FIGS. 5-7 present some particular example embodiments of the inventiveelectronic trim capacitor 10. FIG. 5 shows an electronic trim capacitor10 that can provide capacitive values from 0 pF to 7 pF, in 1 pFincrements. The electronic trim capacitor 10 here corresponds to thedescription of FIG. 4, but specifically contains three parallel branchcircuits 30 containing three capacitors 32 that may be connected acrossthe first capacitor terminal 18 and second capacitor terminal 20 by theswitches 34.

FIG. 6 shows an electronic trim capacitor 10 which can providecapacitive values from 0 pF to 15 pF, in 1 pF increments. The electronictrim capacitor 10 in FIG. 6 is similar to that in FIG. 5, except that afourth branch circuit 30 and an associated 8 pF unit capacitor 32 areadded.

FIG. 7 shows an electronic trim capacitor 10 that can provide capacitivevalues from 0 pF to 31 pF, again in 1 pF increments. The electronic trimcapacitor 10 in FIG. 7 operates under similar principles as that inFIGS. 5-6, except that it adds a fifth branch circuit 30 and anassociated 16 pF unit capacitor 32.

FIG. 8 depicts a capacitor-based high Q structure 110, in use to enhancethe Q of a capacitive circuit 112 which is being employed to tune ageneral circuit 1. Accordingly, the high Q structure 110 connects to the“workpiece” like capacitive circuit 112 at a first node 114 and a secondnode 116, and then connects, in turn, to the general circuit 1 at thesecond node 116 and a third node 118.

The capacitive circuit 112 includes a first resistance 122, acapacitance 124, and a second resistance 126. These “elements” of thecapacitive circuit 112 are intentionally labeled here as electricalproperties rather than as devices, to emphasize that it is propertieswhich are of present interest. For example, the capacitance 124 is thenet capacitive effect of the capacitive circuit 112, rather thannecessarily being the particular capacitance of a single component. Thecapacitance 166 may thus be that of a complex assembly of components,and it particularly includes intrinsic effects due to inter-leadcapacitance, inter-trace capacitance, etc. The capacitance 166 is alsoshown as being variable, because such will be the case for manyapplications, such as tuning circuits like the general circuit 1 in FIG.8. However, it should be appreciated that the capacitance 166 need notbe variable or even be provided by what most might consider aconventional capacitor device.

Similarly, the first resistance 164 and second resistance 126 may bepresent in complex assemblies of components, such as switches andinter-component conductors. The first resistance 164 and the secondresistance 126 are depicted as separate in FIG. 8 to facilitatediscussion of the particular applications described elsewhere herein.The skilled practitioner of the electrical arts will, however, readilyappreciate that the capacitive circuit 112 will exhibit only one netresistance, which will be the sum of the first resistance 164 and secondresistance 126.

Turning now to the high Q structure 110 itself, this includes a parallelcapacitor 128 and a series capacitor 130. As shown, the parallelcapacitor 128 connects across the capacitive circuit 112 at the firstnode 114 and the second node 116. The series capacitor 130 then connectsto the capacitive circuit 112 at the first node 114, and its other endto the third node 118.

FIG. 8 further includes some example component values. Both the firstresistance 122 and the second resistance 126 have values of 0.5 ohmseach; the capacitance 166 has a value of 11 pico farads; the parallelcapacitor 128 has a value of 40 pico farads (pF); and the seriescapacitor 130 has a value of 12 pF. Using the above values and afrequency of 315 mega hertz, the capacitive circuit 112 by itselfexhibits a net capacitance of 11 pF and a theoretical Q of about 10.Unfortunately, a Q of 10 is too low for many applications where it isdesirable to use the capacitive circuit 112, particularly in tuningapplications.

In contrast, continuing with these same example values and furtheremploying the high Q structure 110, the Q of the circuit “seen” by thegeneral circuit 1 at the second node 116 and the third node 118 israised to about 200. This high a Q value is acceptable for manyapplications, particularly many tuning applications. The net capacitance“seen” at the second node 116 and the third node 118 is now about 10 pF(but easily adjustable to 11 pF).

FIG. 9 depicts a capacitor and inductor-based high Q structure 150. Thisalternate embodiment is also shown being used to enhance the Q of acapacitive circuit 152 (possibly the same as the capacitive circuit 112in FIG. 8) as it, in turn, is employed to tune the general circuit 1.The high Q structure 150 connects to the “workpiece” like capacitivecircuit 152 at a first node 154 and a second node 156, much as was thecase in FIG. 8. However, the high Q structure 150 here connects insteadto the general circuit 1 at a third node 158 and a fourth node 160, andincludes an internal fifth node 162.

The capacitive circuit 152 includes a first resistance 164, acapacitance 166, and a second resistance 168, which may be the same ordifferent than those for FIG. 8. However, here also, these arerepresentations of net properties for possibly quite complex assembliesbeing used as the capacitive circuit 152.

The high Q structure 150 here additionally includes a first inductor 170and a second inductor 172. As shown in FIG. 9, the first inductor 170 isconnected in series at one of its ends to the first resistance 164, andat its other end to the fifth node 162. The second inductor 172 isconnected in series at one of its ends to the second resistance 168, andat its other end to the fourth node 160. A parallel capacitor 174 isthen connected in parallel across the fourth node 160 and the fifth node162, and a series capacitor 176 is connected in series between the thirdnode 158 and the fifth node 162.

FIG. 10 depicts a quality factor (Q) enhancing structure (high Qstructure 210, only partially shown) containing an electronic trimcapacitor 212 as its capacitive circuit workpiece. The high Q structure210 might, for example, be the circuit of FIG. 8 or 9, and theelectronic trim capacitor 212 might be the circuit of FIGS. 4-7. Itshould be noted that the inventor anticipates that the electronic trimcapacitor 212 will be componentized into integrated circuits, as shownhere, or constructed as a module, and that it will often be used in themanner shown in FIG. 10.

The electronic trim capacitor 212 has a first power terminal 214 and asecond power terminal 216; a first capacitor terminal 218 and a secondcapacitor terminal 220; and a program terminal 222 and an enableterminal 224. In generally conventional manner for integrated andmodular circuits, the first power terminal 214 and second power terminal216 receive suitable electrical power to operate the electronic trimcapacitor 212. In generally conventional manner for conventionalcapacitors, the first capacitor terminal 218 and second capacitorterminal 220 connect the electronic trim capacitor 212 into the high Qstructure 210. However, quite unlike pre-existing devices, the programterminal 222 and enable terminal 224 are used to accomplish digitalprogramming of the electronic trim capacitor 212.

FIG. 11 is a flow chart depicting the major steps of a programmingmethod 250 used with the electronic trim capacitor 212 of FIG. 10. In aninitial step 252, programming is initiated by setting the enableterminal 224 to a particular electrical state. Suitable choice of anappropriate electrical state and the use of suitable electrical signaltailoring components to insure that spurious enabling of the electronictrim capacitor 212 does not happen are well within the capabilities ofthose skilled in the electronic arts, and will not be discussed furtherhere other than to note that as a security feature a common scenario maybe that initial overall system assembly is the only time when the enableterminal 224 is actually connected, and thus the only time whenprogramming is permitted to occur.

In a step 254 programming continues by supplying an appropriate pulsesignal 226 (FIG. 10) to the program terminal 222. In this manner,supplying a selected number of pulses in the pulse signal 226, while theenable terminal 224 is enabled, will produce a desired total number ofcapacitance increments in the electronic trim capacitor 212. As anothersecurity feature, protection against programming errors may alsoprovided for by the use of conventional electrical circuit mechanismssuch as Schmitt trigger, pull-down, and debounce sub-circuits in theelectronic trim capacitor 212.

Finally, in a step 256, the internal logic of the electronic trimcapacitor 212 sets a capacitive value which is exhibited at the firstcapacitor terminal 218 and the second capacitor terminal 220.

FIG. 12 is graph of how the capacitance value of the electronic trimcapacitor 212 of FIG. 10 changes as a function of the number of pulsesprovided in the pulse signal 226. For this example the electronic trimcapacitor 212 is presumed to be equivalent to the particular electronictrim capacitor 10 of FIG. 5, i.e., being able to supply 0-15 pico farads(pF) in 1 pF increments. At an initial point 260, which is leftmost onthe graph, the electronic trim capacitor 212 exhibits essentially zerocapacitance. In most embodiments, initial enabling at the enableterminal 224 will also operate to reset the electronic trim capacitor212, so point 260 can represent enablement before receipt of any pulsesat the program terminal 222.

At a point 262 a first pulse 228 is supplied in the pulse signal 226 tothe program terminal 222, and (assuming that the enable terminal 224 isenabled) the electronic trim capacitor 212 should accordingly change toprovide one increment of capacitance. The electronic trim capacitor 212therefore internally connects its 1 pF capacitance branch circuit acrossits first capacitor terminal 218 and second capacitor terminal 220, andexternally exhibits 1 pF of capacitance.

At a next point 264 a second pulse 228 is received and the electronictrim capacitor 212 internally disconnects its 1 pF unit capacitance, andinternally now connects its 2 pF unit capacitance, and now externallyexhibits 2 pF of capacitance across its first capacitor terminal 218 andsecond capacitor terminal 220.

At another point 266 a third pulse 228 is received, and the electronictrim capacitor 212 now internally reconnects its 1 pF unit capacitancein parallel with its still connected 2 pF unit capacitance, andexternally exhibits a nominal 3 pF of total capacitance.

And as can be seen at still subsequent points 268-274, as successivepulses 228 are received, the electronic trim capacitor 212 willprogressively exhibit 4 pF, 5 pF (1+4), 6 pF (2+4), and 7 pF (1+2+4).This continues until a point 276 is reached, where the electronic trimcapacitor 212 has completely cycled and returns to exhibiting a nominalzero capacitance across its first capacitor terminal 218 and secondcapacitor terminal 220. Further pulses 228 now simply cause the abovedescribed scenario to repeat. At any point in the programming method250, stopping the pulses 228 at the program terminal 222 or disenablingfurther programming by changing the electrical state at the enableterminal 224 will cause the then present value of capacitance exhibitedacross the first capacitor terminal 218 and second capacitor terminal220 to become fixed.

FIG. 13 is a schematic of a componentized integration of a programmabletrim capacitance 310 into an integrated circuit 312, for use indigitally programming the tuning of an oscillator 301. The integratedcircuit 312 includes an electronic trim capacitor 314, which may be thesame as those described herein with reference to FIGS. 3-7 (electronictrim capacitor 10), and further includes a high Q structure 316, whichmay be the same as that described herein with reference to FIG. 8 (highQ structure 110). Accordingly, the programmable trim capacitance 310 mayalso be programmed as has been described herein with reference to FIGS.10-12 (programming method 250). The programmable trim capacitance 310has a first power terminal 318 and a second power terminal 320; a firstcapacitor terminal 322 and a second capacitor terminal 324; and aprogram terminal 326 and an enable terminal 328. The first powerterminal 318, second power terminal 320, program terminal 326, andenable terminal 328 all may be connected, as stylistically shown, to theelectronic trim capacitor 314 in the manner already described herein forother electronic trim capacitor embodiments. However, since the high Qstructure 316 is included, the electronic trim capacitor 314 connects toit at a first node 330 and a second node 332, rather than directly tothe first capacitor terminal 322 and second capacitor terminal 324. Asshown, the high Q structure 316 is instead what connects to the firstcapacitor terminal 322 and second capacitor terminal 324 here.

The programmable trim capacitance 310 provides a number of benefits. Dueto inclusion of the electronic trim capacitor 314, it provides anelectronically programmable variable capacitance. Due to inclusion ofthe high Q structure 316 it also provides a high quality factor (Q), onecommensurate with the needs of many tuned devices such as the oscillator301. However, as was noted above, the high Q structure 316 is optional,and may be omitted in embodiments or applications where the electronictrim capacitor 314 provides enough Q by itself.

Other benefits of the programmable trim capacitance 310 are provided byits low terminal count and potentially small size. FIG. 13 shows a sixterminal device, and sophisticated terminal-function combinations canreduce this count even further. But even so, this low number ofterminals and current manufacturing techniques permit the integratedcircuit 312 of the programmable trim capacitance 310 shown here to beimplemented in a standard 6 pin SOT type package, making it very smallindeed.

FIG. 14 is a schematic of a componentized integration of a differentprogrammable trim capacitance 410 into a module 412, for use indigitally programming the tuning of an amplifier 401. The module 412includes an electronic trim capacitor 414, which may here also be thesame as those described with reference to FIGS. 3-7 (electronic trimcapacitor 10), and further includes a high Q structure 416, which heremay be the same as that described with reference to FIG. 9 (high Qstructure 150). The programming as described herein with reference toFIGS. 10-12 (programming method 250) may also be used here.

The programmable trim capacitance 410 has a first power terminal 418 anda second power terminal 420; a first capacitor terminal 422 and a secondcapacitor terminal 424; and a program terminal 426 and an enableterminal 428. The first power terminal 418, second power terminal 420,program terminal 426, and enable terminal 428 all may be connected, asshown, to the electronic trim capacitor 414 in already described mannersfor other electronic and programmable trim capacitors. As shown, theelectronic trim capacitor 414 here is connected to the high Q structure416 at a first node 430 and a second node 432, rather than directly tothe first capacitor terminal 422 and second capacitor terminal 424.

The discussion of benefits for the programmable trim capacitance 310 ofFIG. 13 applies in large part equally for the programmable trimcapacitance 410 of FIG. 14. The module 412 type package in FIG. 14,rather than an integrated circuit type package, as in FIG. 13, will bedesirable to facilitate including a first inductor 434 and a secondinductor 436, as shown, in the high Q structure 416. Alternately, if anintegrated circuit type package is desired, small inductance values canbe provided using some integrated circuit fabrication techniques, oradditional integrated circuit terminals and external inductances can beused instead.

FIG. 15 is a stylized block diagram of an exemplary embodimentillustrating internal functions of the electronic trim capacitor 10 withprogramming error protection, which here is implemented as an integratedcircuit 12. The electronic trim capacitor 10 has a first power terminal14 (V_(DD)) and a second power terminal 16 (V_(ss)); a first capacitorterminal 18 (C₁) and a second capacitor terminal 20 (C₂); a programterminal 22 (Program); and an enable terminal 24 (Enable). Also shown inFIG. 15, the integrated circuit 12 of the inventive electronic trimcapacitor 10 has a number of branch circuits 30, each including acapacitor 32 connected in a series arrangement with one or more switches34. In embodiments such as the integrated circuit 12 version shown here,the inventor has used solid state MOSFET devices, but this is not anecessary requirement. FIG. 15 also shows how the inventive electronictrim capacitor 10 further includes an interface 36, a memory 38, and anerror protection subcircuit 40. The interface 36 serves to program theelectronic trim capacitor 10 and the memory 38 serves for retaining thatprogramming. An error protection subcircuit 40 consisting of one or moreSchmitt triggers, pull downs and debounce subcircuits prevents thecapacitor from incorrect programming and is connected to the memory 38and the interface 36. As can be appreciated by those skilled in the art,the programming error protection subcircuit 40 may be configured in avariety of ways in order to prevent undesirable programming of thecapacitor.

In addition to the above mentioned examples, various other modificationsand alterations of the inventive programming method 250 may be madewithout departing from the invention. Accordingly, the above disclosureis not to be considered as limiting and the appended claims are to beinterpreted as encompassing the true spirit and the entire scope of theinvention.

INDUSTRIAL APPLICABILITY

The present programming method 250 is well suited for application inmodem electronic circuits. As electronic systems have becomeincreasingly used throughout many segments of our society and ourpersonal lives, the importance of easy, fast, precise, reliable, andinexpensive methods to trim adjustable capacitances used in such systemshas correspondingly grown in importance.

The inventive method employs relatively few steps, and then only ones ofrelatively limited complexity. It imposes no particular constraints onthe circuits employing it, as can be seen herein with reference to thealso discussed electronic trim capacitor or electronic trim capacitorand high Q structure combinations. The very low six pin total terminalcount (potentially even further reducible) of the electronic trimcapacitor illustrates this point well. he method also facilitatesinclusion of device security features, such as heightened enabling anddisenabling to prevent inadvertent programming and signal conditioningto prevent unreliable programming due to spurious program signal contentlike electronic noise.

In view of the programming method 250 being easy to use, learn, andremember, it is anticipated that those of reasonable, or even minimal,skill in the relevant arts should have relatively little troubleadopting it quickly for productive use.

For the above, and other, reasons, it is expected that the programmingmethod 250 of the present invention will have widespread industrialapplicability. Therefore, it is expected that the commercial utility ofthe present invention will be extensive and long lasting.

What is claimed is:
 1. A method for digitally programming a capacitancevalue for an electronically adjustable trim capacitor, the programmingmethod comprising the steps of: applying a program signal to a programterminal of the electronically adjustable trim capacitor; setting thecapacitance value of the electronically adjustable trim capacitor basedon a logic state corresponding to the applied program signal having atleast one pulse, the logic state corresponding to a number of pulsespresent in the applied program signal; wherein said adjustable trimcapacitor is configured such that said capacitance value is programmedthrough said program signal applied to said program terminal; andwherein the capacitance value of said adjustable trim capacitorincreases by one increment each time a pulse present in the programsignal is received at the program terminal.
 2. The method of claim 1,wherein the logic state of the program signal operates to control aninternal logic of the electronically adjustable trim capacitor operableto adjust the capacitance value of the electronically adjustablecapacitor.
 3. The method of claim 2, wherein the program signal consistsof electronic pulses.
 4. The method of claim 3, wherein at least oneconventional electrical circuit mechanism comprised of a set of at leastone of Schmitt triggers, pull-downs, and debounce sub-circuits is usedas a protection against programming errors.
 5. The method of claim 1,wherein each pulse increases the capacitance value of the electronicallyadjustable trim capacitor by one increment, until a maximum capacitancevalue of the electronically adjustable trim capacitor is reached, atwhich point a next pulse returns the capacitance value of theelectronically adjustable trim capacitor to a minimum value.
 6. Themethod of claim 1, further comprising the steps of: initializing theelectronically adjustable trim capacitor by applying an enable signal toan enable terminal of the electronically adjustable trim capacitor priorto applying the program signal to the program terminal, where withoutsaid enable signal being applied, said program signal has no effect uponthe electronically adjustable tim capacitor.
 7. The method of claim 6,further comprising the step of: disconnecting the enable terminal afterinitial programming, so that no subsequent enable signal is able to beapplied to said enable terminal, and therefore no subsequent programmingcan take place.
 8. The method of claim 6, wherein applying said enablesignal to said enable terminal sets the capacitance value of theelectronically adjustable trim capacitor to a predetermined value. 9.The method of claim 8, wherein the predetermined value is the minimumcapacitance value for the electronically adjustable trim capacitor. 10.The method of claim 9, wherein the minimum capacitance value is nominalzero capacitance.
 11. The method of claim 8, wherein the predeterminedvalue is an intermediate value between the electronically adjustabletrim capacitor's minimum and maximum capacitance values.
 12. The methodof claim 8, wherein the predetermined value is the maximum capacitancevalue of the electronically adjustable trim capacitor.